An Experimental Study on Monotonic Shear Behavior of the Interface between Fine Sea Sand and Steel

The mechanical behavior of the interfaces between fine sea sand and offshore structure is regarded as a quite important issue that influences the foundation-bearing capacity and structural safety. In this work, by employing a modified shear apparatus with a ring-transparent sample container, a series of interface shear tests were conducted to shed light on the effects of the applied normal stress, initial relative density, and the roughness of the steel surface. Based on image analysis, the horizontal deformation at various vertical positions within the sand specimen was captured. In addition, the postshearing particle-size distributions of sand specimens were measured and compared. From the acquired test results, it was demonstrated that for the dense and medium dense sand–steel interfaces, strain softening is a typical shear behavior, regardless of the roughness of the steel surface. The mobilized shear stress of the interface with a smooth steel surface reaches the peak strength earlier than that of the rough one and then rapidly declines to residual strength within a short softening stage. The shearing zone in sand specimens can be divided into a large deformation zone and a small deformation zone. The shear deformation that occurs within the sand specimens sheared against the smooth steel surface is negligible and concentrated very close to the interface. However, for rough surface and dense sand, the interlocking between sand and steel forces the deformation of sand specimens to arise in greater scope and magnitude, accompanied by significant particle crushing.